Although there has been published paper on cooking rice grains, no report has dealt with the measurement of moisture profile in a grain of rice during cooking. In the present study, a non-destructive method of nuclear magnetic resonance (NMR) imaging was applied to the moisture profile in a grain of rice.In the firs attempt, a partly cooked rice grain was quenched after selected period of boiling the moisture distribution in this was observed at room temperature using the two dimensional NMR transverse relaxation time (T2) imaging method. To obtain clear images, we needed two hours to take one moisture image. The measured moisture profile clearly showed that the quenching was successful to reserve the moisture profile to some extent. However, there remained a question of possible water migration from outer high moisture shell into the low moisture core during the long waiting time between the quenching and imaging measurement. This quesiton was explored by a real-time observation. To a
… Morechieve the realtime measurement, we needed to shorten greatly the time required to collect the series of data sets for T2 imaging. We developed a multi-echo application for on-dimensional imaging with double slicing gradient. This method reduced the time of collecting data so short as one minute. This made it possible to observe the change of profile in every minute during boiling. The change of moisture profile was simulated using a mathematical model in which water percolates through a starch cylinder by diffusion. The calculated profile showed a considerable delay in moisture uptake compared with that observed in the experiment. One of the possible cause of this discrepancy is that the gelatinization rate used in the simulation were underestimated.次にリアルタイム測定で得られた炊飯中の米粒内水分変化から糊化過程の分子レベルにおける解明を目指した.米粒を構成する細胞壁の果たす吸水・糊化過程への役割を明確にすべく酵素処理した精白米と無処理の精白米を調整し,偏光顕微鏡観察および炊飯中の水分変化測定を行なった。その結果細胞壁による吸水抑制効果は大きくないことがわかった.このことから米粒を楕円円柱状に成型されたデンプンと見做して,炊飯過程における水分子の移動現象を計算した.計算結果による予測は実験結果よりずっと遅い水分上昇を示しており計算に使った仮定に誤りがあるか或いは拡散係数や糊化速度が実際と異なっていることを示唆しており,更なる研究が必要である. Less